#include <algorithm>
#include <iostream>
#include <numeric>
#include <set>
#include <vector>

using namespace std;

using ll = long long;

int main(void) {
  ll a, b, c, d, e;
  cin >> a >> b >> c >> d >> e;

  if (d - e <= 0) cout << a - b << endl;
  else cout << (a - b) + (d - e) * c << endl;

  return 0;
}